The preparatively important catalytic opening of epoxides to beta-titanoxy radicals via single-electron transfer (SET) is described. These radicals can be reduced to alcohols or participate in C-C bond-forming reactions. A key step in the catalytic cycle is the conceptually novel protonation of titanium-oxygen and -carbon bonds. Our method combines the advantages of radical reactions, e.g., high functional group tolerance and stability of radicals under protic conditions, with the ability of organometallic complexes to determine the course of transformations in reagent-controlled reactions.